The present invention is drawn to a process for regenerating a spent, naturally occurring catalyst and, more particularly, a naturally occurring catalyst having an iron content of from about 10 to 70 wt.% as metal wherein said catalyst has been poisoned and deactivated by the deposition thereon of carbon and metals as a result of the hydroconversion of heavy hydrocarbon feedstocks with a fresh catalyst.
Heretofore there have been known in the art many processes for regenerating catalysts which have been deactivated due to carbon deposition on the catalyst during the hydroconversion of hydrocarbon feedstocks. Typical prior art patents include U.S. Pat. Nos. 2,640,009, 3,755,202, 4,007,131 and 4,026,821. These prior art patents disclose regenerating processes for removing carbon from the deactivated catalyst which consists of burning off the carbon deposits by blowing oxygen in a diluent gas environment over the catalyst at elevated temperatures. Suitable diluent gases disclosed in the prior art for use in the foregoing processes include nitrogen, flue gas and steam. These particular processes dealt only with catalyst deactivation due to carbon deposition. The spent catalysts subjected to the foregoing regeneration process were generally used in the hydroprocessing or the hydroconversion of substantially metal-free feedstocks such as napthas and gas oils. The difference between the processes of the above-identified prior art patents generally involved the type of equipment used, number of stages and the ranges of operating conditions. For example, U.S. Pat. No. 4,007,131 discloses a two step method wherein initially a gas mixture containing about 0.1 to 4 volume percent of oxygen is passed over the spent catalyst at a temperature of about 315.degree. to 650.degree. C., a pressure of greater than 100 psig and a space velocity of higher than 50 LHSV. After the initial step the oxygen concentration was increased to up to 10 volume percent at increasing temperatures. U.S. Pat. No. 4,026,821 discloses a cylindrical shell for supporting the catalyst during regeneration. The catalysts regenerated by the methods of the foregoing patents were catalysts which consist of Group VI, Group VII or Group VIII metals or mixtures thereof on refractory supports. These patents did not deal with the poisoning of catalysts due to metal deposition thereon.
There are also known processes in the prior art for regenerating hydrotreatment and hydroconversion catalysts which have been deactivated by both metal and carbon deposition. Typical of these processes are those disclosed in U.S. Pat. Nos. 4,089,806, 4,122,000, 4,234,452 and 4,454,240. The catalysts regenerated by these processes are catalysts comprising Group VI and Group VIII metals in combination which are supported on inorganic oxide carriers. In the processes disclosed in the foregoing patents, the metal contaminants are removed by employing chemicals prior to carbon burn-off in order to avoid release of sulphur dioxide and sulphurization of the carrier support which would result in damage to the physical properties of the catalyst, namely, pore volume, surface area and crushing strength. These procedures known in the prior art fail to oxidize the metal sulphides formed on the catalysts during operation. This is generally helpful since metal sulphides are generally less soluble than oxides and, therefore, when vanadium is chemically extracted from the spent catalyst the Group VI and Group VIII metals can selectively remain on the matrix. In addition to the foregoing, U.S. Pat. No. 4,182,747 as well as other above-identified patents disclose processes for removing metal contaminants before carbon burning by acid washing of the spent catalyst.
As previously noted the foregoing processes are designed to be used with catalysts containing Group VI and Group VIII metal combinations on refractory supports. These catalysts are very expensive to manufacture. As a result the costly regenerating processes noted above are economical to apply to these catalysts; however, these processes would not be cost efficient as applied on the inexpensive naturally occurring catalysts for which the process of the instant invention is designed.
Accordingly, it is the principal object of the present invention to provide a process for regenerating a spent naturally occurring catalyst which has been poisoned and deactivated by the deposition of carbon and metals.
It is a particular object of the present invention to provide a process as aforesaid wherein the naturally occurring catalyst is characterized by an iron content of about 10 to 70 wt.% as metal.
It is a further object of the present invention to provide a process as aforesaid wherein the regenerated catalyst has physical properties comparable to the fresh naturally occurring catalyst.
It is a still further object of the present invention to provide a process as aforesaid which is efficient and economical for use in regenerating naturally occurring catalysts.
Further objects and advantages of the present invention will appear hereinbelow.